The fastest way to find out whether or not the oil is rancid is to slice open a capsule and take a whif. Source Naturals Krill Oil caps did have bright colored antioxidants inside, though the smell and taste was of an unpleasant old fish. I have yet to find a fish oil I trust. Mabey it's a problem living in such a warm city. Ascenta vege oil is pretty good but very expensive.